Both normal volunteers and persons with ABSD will be studied. Phonation Threshold Pressure (PTP) will be measured using the brief interruption of supraglottal airflow with a valve during phonation into a tube. The electroglottographic signals will be used to determine when vocal fold vibration ceases after the valve closes. The PTP will be measured as the difference between an estimate of the subglottal pressure achieved after phonation offset following valve closure, and the minimum subglottal vocal tract pressure at the point just before vocal fold vibration ceases following the interruption of airflow. Persons with ABSD who have higher phonation threshold pressures than normal will then receive an injection with botulinum toxin injection into the thyroarytenoid muscle on one side based on movement asymmetries observed on fiberoptic nasolaryngoscopy. Blinded measures of symptom frequency made before and after treatment will determine if symptoms are improved.